A variety of robot configurations currently perform various tasks at manufacturing sites. Among these tasks are the picking and placing of objects that are delivered to an initial conveyance device (such as a conveyor belt) upon which the articles may be initially in various random orientations (“initial article picking position”). Known devices for picking and placing articles (hereinafter “pickers”) are entrusted with the task of picking up such articles and re-orienting them into a position (“article placement position”) where each article is properly positioned for at least one subsequent treatment at one or more treatment stations located within a production facility.
Pickers that arrange articles from an initial position to any successive position typically include a robotic arm having a moveable end-effector that is connected to a gripper. A programmable controller moves the robotic arm and gripper to the article, picks up the article by controlling the gripper, moves the robotic arm to at least one successive position and releases the article by controlling the gripper. The robotic arm may, for instance, place the article into a conveyable position for conveyance on a running belt, a vacuum-conveyer, a neck-conveyer or other conveyance means. Alternatively, the robotic arm may place the article into a receptacle with like articles to effect grouping of like articles prior to further processing. For instance, it may place like articles on a pallet for placement of identifying article bar codes on the articles and/or the pallet. In typical configurations, the gripper includes a pick-up mechanism for picking and placing an article. The mechanism may be one of many kinds of tools known to those skilled in the art such as, for example, a magnetic device, a vacuum or suction device, a mechanical device or any other known device, depending on the characteristics of the article to be picked and placed. Once the gripper has picked up the targeted articles, the mechanical device with the gripper moves the items into the desired position and releases the items.
In consideration of the need for pickers to work within a real three-dimensional environment, enhancement to gripping technique can enhance the pickers' ability to accomplish tasks efficiently. Changes to configurations need to account for safe manipulation of an article in the manipulation space (that is, the area necessary to manipulate the object) and the manipulation cost (that is, the necessary time to finish the manipulation). In certain applications, it, therefore, desirable to bring an article from a relatively unknown position and orientation to a known orientation (but possibly unknown position) with minimal means. Assuming an article of an undetermined geometry assumes an initial position in a random configuration and the only force acting on it is gravity, considering the geometry and mass of the article, a robotic arm with a camera could detect the current article picking orientation, pick up the article and then put it in the “proper” article placement position. This approach can be costly if a high throughput is necessary, and, with current gripper configurations, it may be necessary to re-grip an article in order to successfully get it between the article picking and article placement positions.
Original commercial gripper designs addressed this by providing a double-rotation configuration to overcome inherent risks in relation to inertia and article height that were experienced in traditional 90° turning tools. During the picking operation, the grippers pick an article, flip the article vertically through rotation around a horizontal axis, orient the article to a proper processing orientation around a vertical axis, convey the article to a final destination, place the article at the final destination (for instance, upon a conveyor) and release the article in a stable position. Referring to FIG. 1, a standard double-rotation gripper assembly 10 is provided with a pivotable arm 12 having a suction assembly 14 at a free extent thereof for gripping an article (not shown). The article may be picked from a plurality of articles arranged in random orientations along a moving conveyance apparatus such as a conveyor belt (not shown).
The center of mass of gripper assembly 10 is maintained along a vertical axis 16 that is displaced from a vertical axis 18 along which the gripper's center of rotation is disposed. The displacement of the gripper assembly's center of mass relative to its center of rotation contributes heavily to vibratory disturbance due to inertial effects, and thereby decreases the mean time between failures (MTBF) of the overall system. In addition, pivotable arm 12 requires an extended time to stabilize the article vibrations during the robot trajectory, thereby escalating the time increments required to effect proper orientation of articles from their original orientation. The industry standard gripper configuration further includes many interacting parts that require significant investments of time and money for installation, operation and maintenance. In order to improve the speed of reorientation tasks, cooperation by multiple robot pickers is often employed, in which case these factors negatively affect the ability to execute predictable picking operations for multiple installations. Where handling of articles is carried out over long periods of time, all of the aforementioned factors contribute to excess MTBF and further reduce the productivity and reliability of entire production systems.
Another way to increase the overall speed of a system is to implement a multiple gripper (such as multiple suction cups) on the end-effector of a robot. Such multiple grippers can grasp several articles simultaneously from the article picking position to pick-up and place two or more articles at the same time. This solution, however, not only increases the weight of the gripper, but also increases the complexity (and therefore the associated cost, operability and maintainability) of the device, and especially constrains use of the gripper to only a few specific article shapes. The increase in changeover time between different articles effectively diminishes the flexibility of the overall system and defeats any benefit attributable to production speed realized by the multiple gripper configuration.
The search for improved grippers for moving devices has, therefore, continued.